The human visual system has 3 types of sensors: Long-, Medium- and Short-wave sensitive cone mechanisms (referred to as L, M and S, respectively). The interaction of a spectral power distribution (a light) with these sensors:Pk=∫ωC(λ)Qk(λ)dλ  (1)
In (1), C(λ) denotes the spectral power distribution entering the eye, and Qk(λ) for k∈{L, M, S} denotes the cone responses. The integration is over the visible spectrum co (approximately 400 to 700 Nanometers). Note here and throughout the document we adopt the convention that cone responses are vectors denoted by an uppercase P. Given (1) we can, as we show later, find the red, green and blue pixel values in an image that produce a desired colour, to match the colours in the image captured by a digital camera.
In fact, from a colour reproduction perspective, (1) is simplistic in the sense that each of us has unique cone sensitivities. The best colour fidelity would result in a different monitor image for each of us. Of course this is impossible: a colour monitor can produce one image. This image is usually matched to an average observer.